The present invention relates generally to light source driver circuits operable to interface with external temperature sensors. More particularly, this invention pertains to driver circuits supporting both negative temperature coefficient resistor temperature sensing and normally closed bi-metal switch (i.e., bi-metallic strip switch) temperature sensing.
Referring to FIG. 1, a light source (e.g., light emitting diode) driver circuit 100 is configured with an internal negative temperature coefficient (NTC) sensing circuit 102. The internal NTC sensing circuit 102 interfaces with an NTC resistor 104 embedded in a light engine 106. The light engine 106 includes a light source 108 that may be formed from a plurality of LEDs configured in various parallel and series arrangements. The driver circuit 100 includes a constant current source 110 to provide power to the light engine 106 from a power source (not shown). The constant current source 110 may include a controller and a current source tank circuit. The controller is responsive to a temperature signal from the internal NTC sensing circuit 102 to adjust operation and current output of the current source tank circuit. In other words, the constant current source 110 is responsive to the temperature signal from the NTC sensing circuit 102 to adjust a current provided to the light engine 106.
Referring to FIG. 2, a light source (e.g., light emitting diode) driver circuit 200 is configured with an internal bi-metallic strip switch sensing circuit 202. The internal bi-metallic strip switch sensing circuit 202 interfaces with a bi-metallic strip switch 204 embedded in the light engine 206. The light engine 206 includes a light source 108 that may be formed of a plurality of LEDs configured in various parallel and series arrangements. The driver circuit 200 includes a constant current source 110 to provide power to the light engine 206 from a power source (not shown). The constant current source 110 may include a controller and a current source tank circuit. The controller is responsive to a temperature signal from the internal bi-metallic strip switch sensing circuit 202 to adjust operation and current output of the current source tank circuit. In other words, the constant current source 110 is responsive to the temperature signal from the internal bi-metallic strip switch sensing circuit 202 to adjust a current provided to the light engine 206.
Conventional driver circuits are designed to interface with either an NTC resistor as in FIG. 1, or a bi-metallic strip switch as in FIG. 2, but not both. For example, the bi-metal switch may be configured as an interrupter to interrupt power to the light source, whereas the thermistor is configured as a sensor to be monitored and current adjusted as a temperature indicated by the thermistor approaches a predetermined limit.